Amino acid aminotransferases (ATases), which catalyse the last biosynthetic step of many amino acids, may have important physiological functions in during growth in milk. In this study, the aspartate ATase gene () from LM0230 was cloned by complementation into DL39. One chromosomal fragment putatively encoding was partially sequenced. A 1179 bp ORF was identified which could encode for a 393 aa, 432 kDa protein. The deduced amino acid sequence had high identity to other AspC sequences in GenBank and is a member of the Iγ family of ATases. Substrate-specificity studies suggested that the lactococcal AspC has ATase activity only with aspartic acid (Asp). An internal deletion was introduced into the chromosomal copy of by homologous recombination. The wild-type and mutant strain grew similarly in defined media containing all 20 amino acids and did not grow in minimal media unless supplemented with asparagine (Asn). The mutant strain was also unable to grow in or significantly acidify milk unless supplemented with Asp or Asn. These results suggest that only one lactococcal ATase is involved in the conversion of oxaloacetate to Asp, and Asp biosynthesis is required for the growth of LM0230 in milk.


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